Advanced methods for wirelessly recharging batteries for implanted medical devices are needed. The useful lifetime of most implants is constrained by the longevity of the power source. The goal of this program is to implement the development of an UltraSound Electrical Recharging system (USerTM) within a clinically deployed gastric sphincter stimulation system. A successful Phase I will lead to expanded use of an existing therapeutic device, and also demonstrate the potential of USerTM as a power platform for many other implants. This combination of power delivery and therapy is innovative. While the ultrasound transmit and receive technique has long been used for materials testing, to our knowledge it has never been employed for wireless power delivery to medical devices. The proposed project will influence technical capability and hence clinical practice. The present method of recharging implantable batteries has been via electromagnetic induction. Although useful, it has its limitations, such as the depth of tissue through which it can effectively transmt, the use of increasingly crowded electromagnetic frequencies, and the propagation of stray electromagnetic fields into the body and the local environment. Ultrasound recharging can 1) provide another option in cases where the electromagnetic induction method does not suffice, 2) reduce exposure to radiation, and 3) avoid conflicts due to overlapping uses of the same electromagnetic frequencies. The specific aims will deal with questions that must be answered to prove feasibility. The aims are to show that the power required for the application can be delivered within the geometrical constraints of the implant, that the charging circuitry previously developed can be substantially miniaturized to fit into the implant, and to conduct in vivo tests o the system. The wireless power transmission technology is based on well-known principles of ultrasound which is known for its safety in diagnostic applications. The potential advantages include smaller transmitters and receivers, elimination of electromagnetic interference and heating of metal parts, and the transmission of power to deeper sites in the body. This new technique will drive new therapeutic applications, hence improving medical options to combat medical conditions. The USerTM technology will support the NIH mission in its goals of improving human health and reducing healthcare costs. This will be done by minimizing the distress and complications caused by battery replacement operations, by increasing the implant functions via providing more power, by improving patient satisfaction and compliance, and by reducing operations to replace batteries and other components.